This study evaluates the safety and efficacy of the Glaxo-Wellcome drug, 1592U89, (abacavir), in combination with other approved anti-retroviral agents in patients with HIV dementia. It is a randomized, double-blind, placebo-controlled multi-center study, enrolling approximately 90 patients. Patients are recruited from the Johns Hopkins AIDS Clinic or from direct referral to the HIV Neurology Consultation Service. Informed, witnessed, signed consent is obtained from all participants or from the person with durable power of attorney. The double-blind, placebo-controlled phase of the study is 12 weeks. After this phase, patients will be eligible to receive 40 weeks of open label 1592U89 200 mg every 8 hours. Evaluations include neurological and neuro- psychological assessments, concurrent medications, concurrent AIDS- defining illnesses, adverse experiences, activities of daily living assessment, routine safety labs, lymphocyte subset, and plasma virology. The primary efficacy measure is the comparison of standardized neuropsychological tests between standard therapy with and without concurrent 1592U89 therapy. Safety analyses will examine adverse experiences, clinical laboratory abnormalities and vital signs over time. To date, 6 subjects are in the double-blind, placebo-controlled phase of the study, and 2 subjects are in the pre-screen phase of the study (1 subject was screened and did not meet criteria). No significant adverse events have occurred. Efficacy evaluations are currently in progress.